Looks like this isn't matching the password we have for you - give it another try

Remember me for 90 days

Why would this be useful? If you wanted to come back and look up your quotes, or buy anything else from us, you'd find all your details still here, so you wouldn't have to answer all the questions again - a bit of a result

If you don’t know how much monthly data you use on your smartphone, laptop or tablet computer you could be paying for more than you need to for your tariff.

Most of us are used to calculating call minutes but few of us really know how much data a YouTube video clip uses, say, or a Flickr page stock full of photos. In short, it’s important to know how much content we get for our Gigabyte (1GB = 1,024 MB, 1MB = 1,024KB), particularly if we’re accessing Wi-Fi hotspots on a pay-as-you-go basis.

It can be easy to get carried away online watching a film and find yourself quickly bumping up against your provider’s fair usage policy, leading to excess data charges of between 2p and 20p per MB. So check terms and conditions for exceeding your monthly allowance carefully before committing to a particular provider.

Which services use the most data

As a rough rule of thumb, text services are data light; images, medium; audio, medium; and video, heavy, which stands to reason given the complexity of each type of data file. The difficulty is that digital files sizes can vary enormously even within the same medium according to quality and length.

So a multimedia-rich website will obviously consume more of your data allowance than a text-heavy one. An email with a high-res photo attachment will be several MBs larger than one with just simple text. A low-quality audio track will be smaller than a high quality one, and so on.

Generally speaking, even if you only had 500MB data usage allowance on your monthly plan, that should allow you to surf the web for at least an hour a day. But if you love watching high-definition movies on your iPad you’re going to need at least 15GB, assuming you watch 10 movies a month. And music lovers addicted to streaming radio services such as Spotify should bear in mind that just an hour’s listening can use up around 100MB.

In our guide to data usage, have a look at the online activities below and work out how much of each you do a month to calculate your typical usage. You can then compare your estimated usage with the data allowance included with your tariff. Why pay for data you don’t need?

Instant messaging

0.25 – 1MB per hour

Web browsing

1.5 – 25MB per hour

Downloading 100 emails

1 - 10MB

Downloading a photo

20 – 100KB (compressed, low resolution)0.5 – 3MB (high resolution)

Downloading an audio track

3 – 8MB (roughly 1–1.5MB per minute)

Downloading a three minute video clip or film trailer

7 – 50MB

Downloading a movie

700 – 1,500MB

Streaming one hour of video

200 – 500MB

Streaming one hour of audio

50 – 150MB

Top tips for data scrooges

- Set your phone or mobile computer to download email headers only rather than the message body. Most often you can decide whether or not you need to read the whole message from the subject line alone and delete unnecessary emails before paying to download the rest of them.

- When using TV catch-up service like BBC iPlayer, choose the standard optimised for mobile devices rather than desktops. A one hour 50 minute film would be around 1.2GB downloaded to desktop but just 492MB for a mobile.

Top deals for data monsters

The good news for consumers is that the rise and rise of the multimedia smartphone and the consequent increase in data usage has hastened the arrival of ‘all you can eat’ tariffs offering unlimited everything. For example, mobile network operator Three made the bold move of scrapping all its data usage caps in December in a bid to woo more smartphone customers.

On the moneysupermarket.com mobile phones channel you can now get the HTC Desire on Three for £30 a month (before two months cashback deal) on a 24-month contract with unlimited texts, 2,000 call minutes and a whopping 50GB of data. Most other mobile providers currently offer around 500MB to 1GB data allowance as standard.

Three is also offering the iPad Wi-Fi + 3G 16GB for £20 a month (£99 for the computer) on a 24 month contract with 15GB of data.

Please note: Any rates or deals mentioned in this article were available at the time of writing. Click on a highlighted product and apply direct.